Our goal is to elicit the principles of recognition by proteins of single-stranded nucleic acids via X-ray crystallography. Such interactions are central to a variety of cellular (e.g. DNA replication and recombination) and viral (e.g. replication and phage genome packaging) processes. We recently obtained a number of diffraction quality crystals of gene V protein from bacteriophage f1 complexed to a variety of ssDNA oligomers. Partial data sets for two such crystal forms have been collected to 3.0 w and 3.4 w utilizing bending magnet radiation. Structure solution of these crystal forms is in progress along with massive crystallization trials of complexes containing mutant gene V proteins.